In Europe, the U.S., and Japan, equipping a vehicle with prevention safety systems for preventing a traffic accident from occurring has been promoted as an effort to decrease the frequency of vehicle accidents and a fatality rate thereof. Among them, systems for detecting surroundings and warning a driver of danger, such as a pre-crash safety system and a blind spot detection system, attract attention in particular. Devices that detect objects surrounding the vehicle are needed to realize these systems and, for example, a stereo camera module and a millimeter-wave radar module are used. In the case of the former, although the module can be realized at a relatively low cost, there is a problem in detection sensitivity that decreases at night. Meanwhile, in the case of the latter, although such a problem does not occur, the module has not been widely used in popular cars due to a cost, and reduction of the cost has been a problem.
One of factors causing a high cost of the millimeter-wave radar module is a high inspection cost thereof.
FIG. 1 illustrates a configuration example of an integrated circuit (IC) in a millimeter-wave radar module. In the configuration example, the IC includes seven ICs of a signal synthesizer IC 1 that generates a millimeter-wave band signal, a transmitter IC 2 that transmits a millimeter-wave signal, receiver ICs 3 to 6 that receive the millimeter-wave signal, and a baseband integrated circuit (base band) (BBIC) 7 for processing the signal received by the receiver ICs. In this example, the transmitter IC 2 includes a variable gain amplifier (PGA) and a power amplifier (PA) and each of the receiver ICs 3 to 6 includes a low noise amplifier (LNA), a frequency converter (Mixer), and an amplifier (AMP).
An operation of the millimeter-wave radar module will be simply described. Signal power of a millimeter-wave band frequency signal generated by the signal synthesizer IC 1 is amplified in the transmitter IC 2 and the signal is emitted as a radio wave to space by a transmission antenna 8. A signal reflected from a target is received as an electric signal by a reception antenna 9, the signals received by the receiver ICs 3 to 6 are amplified and are then processed in the BBIC 7, and information of the target is detected. The four receiver ICs 3 to 6 exist because the number of reception channels is increased to improve angle detection performance of a radar.
As described above, the reason why the module is configured using the plurality of ICs is to improve the versatility, such that a designer of the millimeter-wave radar module designs a system by combining any transmitter IC and any receiver IC. For this reason, the plurality of high frequency ICs is implemented inside of the millimeter-wave radar module. A millimeter-wave radar system is operated at a very high frequency band such as 24 GHz, 77 GHz, and 79 GHz. For this reason, an inspection cost at the time of an IC shipment has been a problem due to restriction such as construction of a test environment that can handle a millimeter-wave band, test precision because of using a high frequency probe or a high frequency socket, and a test time. Particularly, since a signal source of the millimeter-wave band is not incorporated in the transmitter IC and the receiver IC, a millimeter-wave band signal needs to be supplied from a measurer and a test cost further increases.
Technology for reducing a test cost in an inspection at the time of a shipment in an IC operated at a high frequency band is described in PTL 1. In PTL 1, an input impedance matching circuit having an inductor, a transistor amplifying an input signal having passed through the input impedance matching circuit, and a transistor for negative resistance capable of being turned on/off by a switch in the input impedance matching circuit are provided. In a test mode, the negative resistance is turned on and a test high frequency oscillator is configured and in a normal operation mode, the negative resistance is turned off and an operation of the oscillator is stopped. As a result, a high frequency characteristic of the IC can be guaranteed by providing a built-in test high frequency signal and only monitoring a direct-current characteristic.